The subject application is directed to a mover system for moving objects and more particularly to a mover system for moving objects having a plurality of independently controlled movers operating along an adjustable predetermined pathway.
Mover systems for transporting objects to or from a location historically used humans to directly control the movers, such as carts, forklifts, pallet jacks and overhead cranes. Movers, such as overhead cranes, often used to deliver objects to selected areas within an industrial facility have been automated by gantry systems that typically utilize pulling chains in the X and Y directions to control the path of the objects being transported to a desired location. Many times such automation incorporates rotary motors that operate to adjust the pulling chains while an operator uses levels to target deliveries. In the most automated application of a gantry system, a control system, such as a motion coordinate control system, is used in combination with a human machine interface (HMI) to allow an operator to identify an end point, such as a point on a floor map, and the master controller programmatically operates to transport the object to the identified location.
Assembly systems are often highly automated having programmable control systems, such as PLCs, connected by network cable to a number of servomotors, running chains, conveyers, tracks, mechanical assemblies and the like. The data connections between such components are generally high-speed, time synchronized, deterministic links for obtaining the maximum performance of the assembly system. Network cable has been preferred over wireless connections because it offers higher data reliability with the least chance of outside interference that can cause a loss of data packets being transmitted across the network. If enough packets are lost in a sequence, an entire assembly operation could fail or error.
Assembly systems have also been developed that take the form of an oval shaped platform stand where a chain drives a series of movers to transport objects to various end points, such as mounted tool stands, for receiving machining or assembly operations. Such operations typically require a high degree of position accuracy and repeatability. Accordingly, it is common to stop the mover and tightly pin the object being transported to a stable platform, perform the desired operation, unpin the object and start the mover to advance the object to its next end point (location). This operation typically requires movers or objects thereon to be precisely positioned for pinning. In many operations the tooling stands operate independently of the master controller and their operation can be signaled to start by mechanical means such as a switch or a photo eye. Some operations, especially those moving at high speeds, require the various tooling stands to be under the command of a common master controller so their operations are time synchronized to perform a specific tooling function in a unified movement. A problem with many such moving systems, such as chain based systems, is that all the movers and tooling stands must operate at the same line speed. If a problem is encountered the entire operation can be interrupted or stopped.
Another moving system that has been developed for increasing speed and flexibility of an assembly line operation, includes a master controller connected, such as by a network cable, to a plurality of linear motors arranged generally along an oval rail system for guiding and commanding multiple magnetic movers. Such systems operate whereby multiple electrical motor wire coils are arranged along the track perpendicularly to the line of travel and with one coil place next to the next coil to form a linear length of coils. When the coils are powered with varying electrical current a magnetic field is produced which reacts to a magnetic field created by a plate of magnets attached to a mover to cause movement of the mover. By scheduling the amount of current to each linear motor coil in succession, one can control the forward or reverse movement of the mover. The movers each include bearing based wheels and run on a guiding rail system that can be made out of plastic, rubber or metal. A key constraint of such magnet moving systems is the distance between the movers that can run together along the direction of rail due to the mechanical design of the mover length and by the magnetics of the linear motor stage design control ability.
Another disadvantage with both chain based or magnet moving systems is that the vector path that the movers travel is essentially mechanically fixed for the life of the machine and is not easily reconfigurable without a major redesign of the entire production system. In addition, with respect to magnetic moving systems, the rail system must follow the entire vector looped path, which adds expense to the system. Further, when a bearing begins to wear on one of the movers due to the wheels running along the guiding rail system, there is generally not an easy automated way to remove that mover from a looped configuration without stopping the entire machine for maintenance. For many applications there is also a need for positional accuracy and repeatability requiring independent mover control all the way around the rail system to achieve the maximum product throughput from the system. Because of this need for maximum product throughput, linear motors must be placed around the entire rail system, including the curves, so that the mover travels at a constant rate. This high rate of speed, particularly around curve sections, increases wear of the support wheels connecting the mover to the rail as well as requiring significant bracing or support of the object to prevent centripetal forces from dislodging or ejecting the object from the mover as it travels along the curve section of the track.
With the advent of robots, robotic autonomous guided vehicle (AGV) systems have been developed that are configured as forklifts or carts that allow for the safe transportation of objects without the need for operators to directly control them or the need for fixed rail tracks. Such robotic control systems include a human-machine-interface for allowing an operator to input modifications to the robotic operation, such as to direct the robotic mover to pick up and transport objects, such as bulk quantities of raw material, to be delivered to a specified end point (location). The assembly area control system may also be programmed automatically to order shipments via wireless signals when a robotic mover is needed. While such robotic movers can be commanded to run at certain speed, they do not operate under a time scheduled control of a motion plan and do not always follow the same path to go to an assigned end point (destination). Robotic movers of an AGV system are also designed to stop, avoid and steer around humans or other obstacles that occur along their path of travel which changes the time that the mover arrives at an assigned end point. Thus, while the mover may be directed to go to a certain end point (location) there is no specific time goal (scheduled time) as to when it is to arrive. Accordingly, the movers of an AGV system do not operate to speed up automatically if they are behind schedule, often caused because a mover's wheels slip on the warehouse floor or if it had to stop and steel around an obstruction on the way to get to the designated end point. Thus, there is often a significant difference in time between when a mover arrives at a designated end point and when the mover is scheduled to arrive at the end point.
The network connection often employed to communicate with an AGV system is standard off-the-shelf secured wireless technology that may already exists in the facility. The connection is designed to use as little network bandwidth as possible. Since an AGV mover has the ability to operate autonomously for some period of time, it is not necessary to be in constant real time communication with the master controller and therefore some data packets being transmitted are lost, not acknowledged and retried over time. Further, the path tracking systems of most AGV systems operate in very coarse increments and are meant to deliver large objects to an end point. Some AGV path tracking systems use navigation devices such as magnets or other markers positioned on the floor to indicate pathways, rooms and no-go zones while other tracking systems are preprogrammed floor map based systems. Most of the preprogrammed floor map based systems require a preexisting floor map of the path space and operate to train the robotic mover where any boundaries lie within the control area. Directional sensors, such as laser or sonar, are used during training to help map additional permanent fixtures that are not on the floor plan (such as desks, partitions, and machinery, etc.). Without such sensors, an AGV mover would often get “lost” during operation because the rotary servo driving the wheels of the mover would not account for errors such as wheel slippage. Typically, an AGV system operates to maintain an approximate location of a mover by comparing what a sensor or set of sensors detect of the walls and/or fixed objects located within the control area to a floor map taking into the account the number of rotations of the mover's wheels taken since the last accurate position. Unfortunately, such path tracking systems are not as effective for large amorphous control areas, such as a warehousing location, where there are not as many fixed unmovable objects to compare against a map. One solution to this problem that has been used is to employ a second sensor or set of sensors that scan certain features, such as ceiling lighting, and adding this information to the AGV's position to map for comparison. However, while this increases the accuracy of the tracking, it also increases the cost of operation and does not provide the needed accuracy for all applications.
Global position satellite systems (GPS) have been developed and are accurate enough for most outdoor purposes. Unfortunately, GPS signals generally cannot penetrate ceilings and walls making such systems unacceptable for most robotic path tracking systems. Various other systems and methods have also been developed using different sensors and include, for example, the use of a compass to map the magnetic signature of various locations against the floor plan map; using multiple Wi-Fi hub signals strength to a fingerprint of each location against a floor plan map; counting the steps and inferring directions a mover is moving; and using a camera to compare pictures to a map. However, none of these location methods have proven accurate enough by themselves for many applications. Further, while in certain control areas the path tracking systems do operate to provide the needed accuracy in to determine the location of a mover along a path, there is no ability to adjust the path parameters or the path of travel of a mover to ensure that the mover arrives at an end point at a specified or scheduled time.
For many applications, assembly or manufacturing systems require positioning systems that are reliable and precision accurate (at least 0.5 mm accuracy) at end points. Wireless, GPS and conventional Radio Frequency identification (RFID) signal strength triangulation systems have been employed and are relatively inexpensive. However, they often do not provide the required accuracy at critical end points. Visual systems may provide the needed accuracy, they require the sensors to have an unobstructed line of sight which can be relatively difficult to obtain and expensive for use with various equipment layouts in certain applications. Accordingly, they have been used primarily to focus on small areas for synchronizing product transfer between two different pieces of equipment. Magnetic tape or optical scale markers have been used in end points with linear slides and with automated guided vehicles but are often difficult to use along an entire predefined path or to achieve the desired accuracy at speed. Further, free operating movers that stray off the predefine path can get lost and are unable to automatically return to their predefined path. While mover systems operating using a track with linear motors have been developed with a plurality of fixed placed electronic sensors positioned along the track as necessary to get the desired accuracy, this technology can only be read as a mover travels along the fixed predefined path.
Accordingly, what is needed is a mover system for transporting objects and more particularly to a mover system for transporting objects having a plurality of independently controlled movers operating along an adjustable predefined virtual vector pathway; that allows an operator to easily modify the path of one or more of the movers; that has a system that operates to modify the movement (path parameters and the mover's path of travel) of each mover to ensure that each mover arrives at a predetermined end point (destination) at a predetermined specified or scheduled time; and has the required accuracy for synchronizing the movement (precise location and arrival times at end points) of the movers.